(a) Field of the Invention
The present invention relates to a liquid crystal display and a driving method thereof, and more specifically, to a thin film transistor liquid crystal display and a driving method thereof.
(b) Description of the Related Art
A thin film transistor liquid crystal display (TFT-LCD) is a display that shows desired images by forming an electric field on a layer of liquid crystals injected between two substrates, and controlling the amount of light transmitted through the substrates by changing the intensity of the electric field. The TFT-LCD is popular as a display to replace the widely used cathode ray tube (CRT) because of its power consumption, thinness, and high resolution, etc.
FIG. 1 is a representation of a TFT-LCD configuration with a circuit diagram. As shown in FIG. 1, the TFT-LCD comprises a liquid crystal panel 10, a gate driver 20, and a data driver 30.
The liquid crystal panel 10 comprises a plurality of gate lines (G1, G2, . . . , Gn) and a plurality of insulated data lines (D1, D2, . . . , Dm) crossing the gate lines, and there are a plurality of TFTs 12, each TFT area (pixel) surrounded by a gate line and a data line. A gate electrode, a source electrode, and a drain electrode of the TFT are connected to a gate line, a data line, and a pixel electrode (not shown) respectively.
The gate driver 20 applies a gate voltage to the gate line to turn the TFT on/off. The gate-on voltage is sequentially applied to the gate lines of the liquid crystal panel, and accordingly, the TFTs connected to the gate lines turn on as the gate-on voltage is applied to. The data driver 30 applies a data voltage for image signals to each data line.
The TFT-LCD is operated by applying the gate-on voltage to the gate electrode connected to the desired gate line so as to switch on the TFT, and by applying the data voltage for an image signal to the source electrode through the data line so that the data voltage reaches the drain electrode. The data voltage is transmitted to the pixel electrode, and an electric field is formed by a potential difference between the pixel electrode and the common electrode. The intensity of the electric field is controlled by the amount of data voltage, and the amount of light transmitted through the substrate is controlled by the intensity of the electric field.
But as the TFT-LCD becomes larger, parasitic capacitance of each data line increases. Then, the data voltage applied to the data lines is not enough to charge the data lines, as shown in FIG. 2.
In FIG. 2, (a) and (b) show the wave forms of data voltage (Vd) applied to odd data lines and even data lines, and of voltage (Ve) charged to the data lines. As shown in FIG. 2 (a) and (b), the data voltage (Vd) applied from the data driver 30 is significantly changed by the parasitic capacitance element from the voltage (Ve) actually charged to the data lines. That is, it takes a significant amount of time (tr) to charge the data lines to a predetermined voltage, and therefore, each pixel cannot be charged with enough data voltage.